New products control rice weevil

Harry Cline Farm Press Editorial Staff | Oct 06, 2001

The loss of Furadan for rice weevil control a year ago was a major blow to California rice producers, but two new replacement products, Dimilin and Warrior, are working well, according to University of California, Davis entomologist Larry Godfrey.

However, Godfrey told producers at the recent Rice Field Day at the Biggs, Calif., Rice Experiment Station that with the new products comes a new application scenario since these new compounds target adults and not larvae like Furadan.

“Timing of application is crucial,” said Godfrey. Monitoring for infestation levels also becomes critical, and the UC entomologist is testing a weevil trap developed for Arkansas rice producers.

Applying the new products too late runs the risk of controlling adults after they have deposited eggs. Too early runs the risk of the compounds dissipating before adults infest fields.

Godfrey's trials showed that Dimilin applied at first rice emergence through 50 percent emergence provided an increasing amount of rice weevil control, peaking at 83 percent. Late timing five and 10 days after 50 percent emergence were slightly less efficacious, he said.

While Warrior and Dimilin alone can control rice water weevil, timing can be “fairly unforgiving. The combination may widen the window of application,” Godfrey said.

The entomologist said Warrior offers immediate adult control while Dimilin may lengthen the residual control by reducing deposition of viable eggs for a longer period of time.

Results of study

Results in 2000s, said Godfrey, show no disadvantage or clear-cut advantage. He is evaluating 2001 studies.

Although Warrior's manufacturer does not recommend the use of its product as a pre-plant application, Godfrey said he has recorded good control using this method, which he says may be easier and more environmentally sound than post-flooding. However, it is not registered for this application method.

One of the issues with rice water weevil control is residual efficacy of these new products, and when it might be necessary to re-treat.

Godfrey said once rice reaches the sixth leaf stage, rice water weevil damage is not likely.

The in-field monitoring trials Godfrey is conducting uses a flagged and floating rice water weevil trap developed in Arkansas.

He is trying this because the scarring thresholds used for applying Furadan are not applicable to Dimilin and Warrior.

The Arkansas trap is useful under that state's delayed flooding production system, and Godfrey is testing it under California's flood production system.

In trials last year, Godfrey validated a relationship between adults captured and larval populations: one adult per trap corresponded to 3.3 larvae trap. He is continuing to evaluate the trap for its efficiency under rice water weevil pressure. He tested it in 10 locations this season.